For example, the various Lower Palaeozoic and Devonian formations on the stable interior platform of North America have presented many problems of correlation largely because the different facies are diachronous.

Athyrids were most abundant during the Silurian and Devonian periods, but still remained common during the early Carboniferous, and even as late as the Permian.

The plate tectonic model of Loeschke et al. invokes crustal rifting during the Ordovician and formation of a Silurian to Devonian ocean that underwent closure during the Devonian-Carboniferous.